Comparative Study of Bulk and Nanoscale BiVO₄ Photoanodes in Photoelectrochemical Oxidation Reactions

Most BiVO₄-based photoelectrodes are prepared using the metal-organic decomposition (MOD) method, which produces a characteristic porous bulk BiVO₄ film. To study different photoelectrochemical (PEC) properties depending on the structure of BiVO₄, bulk- and nanoscale (nano)-BiVO₄ photoelectrodes are prepared using the same MOD method on compact-SnO₂ (c-SnO₂) and c-SnO₂/mesoporous-SnO₂ electrodes, respectively. Unlike the well-known film structure of bulk-BiVO₄, nanoscale dots of BiVO₄ are formed on the surface of the mesoporous SnO₂ particulate film, as confirmed by absorbance, X-ray diffraction (XRD), and transmission electron microscope (TEM) measurements. The PEC behavior of both BiVO₄ photoanodes is examined for glycerol and sulfite oxidation reactions. The optimized bulk- and nano-BiVO₄ PEC cells recorded photocurrents of 2.37 and 4.01 mA cm⁻² for glycerol oxidation and of 3.28 and 5.19 mA cm⁻² for sulfite oxidation, respectively. The excellent photocurrent generation ability of the nano-BiVO₄ electrode can be used to design an ideal BiVO₄-based PEC cell. Impedance analysis is performed to explain the differences in charge transfer/transport between bulk- and nano-BiVO₄ PEC reactions and the reason behind the enhanced performance of nano-BiVO₄ compared to its bulk counterpart.